This section provides background information related to the present disclosure which is not necessarily prior art.
High-energy density, electrochemical cells, such as lithium-ion batteries can be used in a variety of consumer products and vehicles. Typical lithium-ion batteries comprise a first electrode (e.g., a cathode), a second electrode (e.g., an anode), an electrolyte material, and a separator. Often a stack of lithium-ion battery cells are electrically connected to increase overall output. Conventional lithium-ion batteries operate by reversibly passing lithium ions between the negative electrode and the positive electrode. A separator and an electrolyte are disposed between the negative and positive electrodes. The electrolyte is suitable for conducting lithium ions and may be in solid or liquid form. Lithium ions move from a cathode (positive electrode) to an anode (negative electrode) during charging of the battery, and in the opposite direction when discharging the battery. Each of the negative and positive electrodes within a stack is connected to a current collector (typically a metal, such as copper for the anode and aluminum for the cathode). During battery usage, the current collectors associated with the two electrodes are connected by an external circuit that allows current generated by electrons to pass between the electrodes to compensate for transport of lithium ions.
Many different materials may be used to create these components for a lithium-ion battery. By way of non-limiting example, cathode materials for lithium batteries typically comprise an electroactive material which can be intercalated with lithium ions, such as lithium-transition metal oxides or mixed oxides of the spinel type, for example including spinel LiMn2O4, LiCoO2, LiNiO2, LiMn1.5Ni0.5O4, LiNi(1−x-y)CoxMyO2 (where 0<x<1, y<1, and M may be Al, Mn, or the like), or lithium iron phosphates. The electrolyte typically contains one or more lithium salts, which may be dissolved and ionized in a non-aqueous solvent. The negative electrode typically includes a lithium insertion material or an alloy host material. Typical electroactive materials for forming an anode include lithium-graphite intercalation compounds, lithium-silicon intercalation compounds, lithium-tin intercalation compounds, lithium alloys and lithium titanate Li4+xTi5O12, where 0≦x≦3, such as Li4Ti5O12 (LTO), which may be a nano-structured LTO. Contact of the anode and cathode materials with the electrolyte can create an electrical potential between the electrodes. When electron current is generated in an external circuit between the electrodes, the potential is sustained by electrochemical reactions within the cells of the battery.
Lithium transition metal based oxides, especially lithium manganese-based oxides like spinel LiMn2O4, LiMn0.33Ni0.33Co0.33O2, LiMn1.5Ni0.5O4, and other Li-rich materials, are promising active cathode materials for lithium-ion batteries as power sources, especially in Hybrid Electric Vehicles (HEVs) and Electric Vehicles (EVs). These materials have been extensively studied as positive electrode materials because of their lower costs, high rate capability, and higher thermal stability as compared with traditional LiCoO2. However, there remain certain outstanding challenges to using these materials in lithium-ion batteries, especially in electric vehicles. One issue is capacity fade, especially when the positive electrode comprises manganese-containing materials.
Thus, while lithium manganese-based materials and other lithium transition metal oxides are promising active materials for high power lithium-ion batteries, the current shortcomings prevent their widespread commercial use, especially in vehicle applications. For long term and effective use, it would be desirable to improve electrochemical cells that employ such active materials to avoid or minimize capacity fade and loss, while employing the desirable aspects of these active materials that provide durable, long-lifetime lithium-ion batteries having lower costs, high rate capability, high current efficiency, and higher thermal stability.